Nectar Production Rates Research Articles

Nectar and floral morphology differ in evolutionary potential in novel pollination environments.

Plants can evolve rapidly after pollinator changes, but the response of different floral traits to novel selection can vary. Floral morphology is often expected to show high integration to maintain pollination accuracy, while nectar traits can be more environmentally sensitive. The relative role of genetic correlations and phenotypic plasticity (PP) in floral evolution remains unclear, particularly for nectar traits, and can be studied in the context of recent pollinator changes. Digitalis purpurea shows rapid recent evolution of corolla morphology but not nectar traits following a range expansion with hummingbirds added as pollinators. We use this species to compare PP, heritability, evolvability and integration of floral morphology and nectar in a common garden. Morphological traits showed higher heritability than nectar traits, and the proximal section of the corolla, which regulates access to nectar and underwent rapid change in introduced populations, presented lower integration than the rest of the floral phenotype. Nectar was more plastic than morphology, driven by highly plastic sugar concentration. Nectar production rate showed high potential to respond to selection. These results explain the differential rapid evolution of floral traits previously observed in this species and show how intrafloral modularity determines variable evolutionary potential in morphological and nectar traits.

Theoretical Advances in the Ecology and Evolution of Mutualistic Interactions – Review of a Symposium (SYMP 14) Organized at ESA + CSEE 2022 Joint Meeting

Theoretical Advances in the Ecology and Evolution of Mutualistic Interactions – Review of a Symposium (<scp>SYMP</scp> 14) Organized at <scp>ESA</scp> + <scp>CSEE</scp> 2022 Joint Meeting

ATLANTIC POLLINATION: a data set of flowers and interaction with nectar-feeding vertebrates from the Atlantic Forest.

Flowering plant species and their nectar-feeding vertebrates exemplify some of the most remarkable biotic interactions in the Neotropics. In the Brazilian Atlantic Forest, several species of birds (especially hummingbirds), bats, and non-flying mammals, as well as one lizard feed on nectar, often act as pollinators and contribute to seed output of flowering plants. We present a dataset containing information on flowering plants visited by nectar-feeding vertebrates and sampled at 166 localities in the Brazilian Atlantic Forest. This dataset provides information on 1902 unique interactions among 515 species of flowering plants and 129 species of potential vertebrate pollinators and the patterns of species diversity across latitudes. All plant-vertebrate interactions compiled were recorded through direct observations of visits, and no inferences of pollinators based on floral syndromes were included. We also provide information on the most common plant traits used to understand the interactions between flowers and nectar-feeding vertebrates: plant growth form, corolla length, rate of nectar production per hour in bagged flowers, nectar concentration, flower color and shape, time of anthesis, presence or absence of perceptible fragrance by human, and flowering phenology as well as the plant's threat status by International Union for Conservation of Nature (IUCN) classification. For the vertebrates, status of threat by IUCN classification, body mass, bill or rostrum size are provided. Information on the frequency of visits and pollen deposition on the vertebrate's body is provided from the original source when available. The highest number of unique interactions is recorded for birds (1771) followed by bats (110). For plants, Bromeliaceae contains the highest number of unique interactions (606), followed by Fabaceae (242) and Gesneriaceae (104). It is evident that there was geographical bias of the studies throughout the southeast of the Brazilian Atlantic Forest and that most effort was directed to flower-hummingbird interactions. However, it reflects a worldwide tendency of more plants interacting with birds compared with other vertebrate species. The lack of similar protocols among studies to collect basic data limits the comparisons among areas and generalizations. Nevertheless, this dataset represents a notable effort to organize and highlight the importance of vertebrate pollinators in this hotspot of biodiversity on Earth and represents the data currently available. No copyright or proprietary restrictions are associated with the use of this data set. Please cite this data paper when the data are used in publications or scientific events.

The Evolution of Resource Provisioning in Pollination Mutualisms.

AbstractResource dynamics influence the contemporary ecology of consumer-resource mutualisms. Suites of resource traits, such as floral nectar components, also evolve in response to different selective pressures, changing the ecological dynamics of the interacting species at the evolutionary equilibrium. Here we explore the evolution of resource-provisioning traits in a biotically pollinated plant that produces nectar as a resource for beneficial consumers. We develop a mathematical model describing natural selection on two quantitative nectar traits: maximum nectar production rate and maximum nectar reservoir volume. We use this model to examine how nectar production dynamics evolve under different ecological conditions that impose varying cost-benefit regimes on resource provisioning. The model results predict that natural selection favors higher nectar production when ecological factors limit the plant or pollinator's abundance (e.g., a lower productivity environment or a higher pollinator conversion efficiency). We also find that nectar traits evolve as a suite in which higher costs of producing one trait select for a compensatory increase in investment in the other trait. This empirically explicit approach to studying the evolution of consumer-resource mutualisms illustrates how natural selection acting via direct and indirect pathways of species interactions generates patterns of resource provisioning seen in natural systems.

Pollination by hummingbirds of Vriesea gigantea (Bromeliaceae) populations in Southern Brazil

Abstract The pollination syndrome hypothesis usually does not successfully apply to the diversity of floral phenotypes or help predict the pollinators of most plant species. In Bromeliaceae, there is a wide range of floral visitors, making its species ideal to test for a correlation between nectar and floral traits with pollination syndrome. In this study, we analyzed the floral features, nectar production patterns, pollinators and floral visitors of Vriesea gigantea, and discussed its potential adaptive and ecological significance. We study three natural populations from the Atlantic Forest, Southern Brazil. The species presented protogyny and herkogamy, and its anthesis occurred at different periods among different populations. Vriesea gigantea has a relatively constant rate of nectar production during the day that continues overnight but at a reduced rate. Newly opened flowers already have around 80.0 μl of nectar. Although classified as chiropterophilous, based on flower morphology and pollinator observations, our results show that hummingbirds are effective pollinators in the studied populations of V. gigantea.

Dynamics of a plant-nectar-pollinator model and its approximate equations

This paper studies effect of nectar on pollination-mutualisms. By rigorous analysis on a plant-nectar-pollinator model, we demonstrate mechanisms by which the decay rate of nectar, the nectar-consumption rate by pollinator and the nectar-production rate by plant could lead to persistence/extinction of pollination-mutualisms. For example, (i) when the decay rate is small, the pollinator survives in the system and pollination-mutualisms persist, in which the plant approaches an enhanced density. (ii) When the decay rate is intermediate, the pollinator can survive in the system only if the initial density of nectar is not below a threshold. (iii) When the decay rate is large, the pollinator goes to extinction even though the plant and nectar persist. Furthermore, we study the approximate equations of the model, in which nectar is assumed to rapidly approach a steady state. We exhibit complete analysis on the equations, which extends previous results. A new finding in comparing the two models is that the initial value of nectar plays a role in persistence of pollination-mutualisms. Our results coincide with experimental observations while numerical simulations confirm and extend the results.

Evolutionary ecology of nectar.

Floral nectar is an important determinant of plant-pollinator interactions and an integral component of pollination syndromes, suggesting it is under pollinator-mediated selection. However, compared to floral display traits, we know little about the evolutionary ecology of nectar. Combining a literature review with a meta-analysis approach, we summarize the evidence for heritable variation in nectar traits and link this variation to pollinator response and plant fitness. We further review associations between nectar traits and floral signals and discuss them in the context of honest signalling and targets of selection. Although nectar is strongly influenced by environmental factors, heritable variation in nectar production rate has been documented in several populations (mean h2 = 0.31). Almost nothing is known about heritability of other nectar traits, such as sugar and amino acid concentrations. Only a handful of studies have quantified selection on nectar traits, and few find statistically significant selection. Pollinator responses to nectar traits indicate they may drive selection, but studies tying pollinator preferences to plant fitness are lacking. So far, only one study conclusively identified pollinators as selective agents on a nectar trait, and the role of microbes, herbivores, nectar robbers and abiotic factors in nectar evolution is largely hypothetical. Finally, there is a trend for positive correlations among floral cues and nectar traits, indicating honest signalling of rewards. Important progress can be made by studies that quantify current selection on nectar in natural populations, as well as experimental approaches that identify the target traits and selective agents involved. Signal-reward associations suggest that correlational selection may shape evolution of nectar traits, and studies exploring these more complex forms of natural selection are needed. Many questions about nectar evolution remain unanswered, making this a field ripe for future research.

Intraflower variation in nectar secretion: Secretion patterns and pollinator behavior in male- and female-phase flowers.

Plants that secrete abundant nectar attract many pollinator visits, potentially leading to a high frequency of geitonogamous pollination. However, intraflower variation in nectar volume might enhance early departure from the flower or inflorescence, reducing geitonogamy. To examine the adaptive significance of multiple nectar-producing spurs within flowers, we related intraflower variation in nectar characteristics to pollinator foraging behavior and plant reproductive success in protandrous Aquilegia buergeriana var. oxysepala. We investigated if nectar volume and sugar mass relate to spur length and if intraflower variation in nectar characteristics differ between male- and female-phase flowers. Because male function requires more pollinator visits than female function, male-phase flowers are expected to have greater nectar volume and lower intraflower variation in nectar volume than female-phase flowers. We used intraflower variation in spur length as an indicator of variation in nectar characteristics and investigated how spur length variation affects pollinator behavior, pollen removal, and seed production. Male-phase flowers had greater nectar volume and lower intraflower variation in nectar volume than female-phase flowers. Intraflower variation in spur length reduced the duration of bumblebee visits. Short visits reduced seed production, but increased pollen removal. Our results suggest that high intraflower variation in nectar production rate can reduce geitonogamy and potentially increase the genetic diversity of pollen received. Such pattern of nectar secretion within and among flowers may allow flowers to ensure effective pollen transfer or high seed production.

Nectar secretion of RN-type cytoplasmic male sterility three lines in soybean [Glycine max (L.) Merr.

Significant progress has been achieved in the use of heterosis in soybean and several soybean hybrids have been released in China. However, broad use of hybrid soybean seed is limited due to low seed setting of female parents. Breeding cytoplasmic male sterile (CMS) lines with high out-crossing rate is necessary to solve the problem. The objective of this study was to determine the relationship between out-crossing rate of CMS lines and their nectar secretion. The daily nectar secretion rhythm, meteorological effect on nectar secretion, and differences in nectar secretion among genotypes and years were investigated in 27 soybean CMS lines (A-lines) with their maintainers (B-lines) and restorers (R-lines). The correlation between out-crossing rate of CMS lines and nectar production was also evaluated. Nectar secretion had diurnal variation. Secretion initiated at about 06:00 for most materials and reached a peak at 07:00–08:30 after flower opened, then the nectar secretion decreased gradually. A sub-peak appeared at about 13:00, while the nectar could not be detected at 17:00. Nectar secretion was greatly influenced by the weather conditions. The amount of nectar secretion increased gradually over time during periods of high temperature and no rainfall for several days. Rainy weather and low temperatures inhibited nectar secretion. There were obvious variations of nectar amount among different genotypes tested. Significant nectar variation within a genotype among years was also observed, and the highest nectar secretion was 3-fold higher than the lowest. The amount of nectar secretion from R-lines was significantly higher than that of A- and B-lines. There was no significant difference in nectar secretion between A- and B-lines. A- and B-lines with higher out-crossing rates secreted more nectar. The amount of nectar secretion of A- and B-lines were significantly positively correlated with the out-crossing rate of A-lines.

Nectar replenishment maintains the neutral effects of nectar robbing on female reproductive success of Salvia przewalskii (Lamiaceae), a plant pollinated and robbed by bumble bees.

It has been suggested that the dynamics of nectar replenishment could differ for flowers after being nectar robbed or visited legitimately, but further experimental work is needed to investigate this hypothesis. This study aimed to assess the role of nectar replenishment in mediating the effects of nectar robbing on pollinator behaviour and plant reproduction. Plant-robber-pollinator interactions in an alpine plant, Salvia przewalskii , were studied. It is pollinated by long-tongued Bombus religiosus and short-tongued B. friseanus , but robbed by B. friseanus . Nectar production rates for flowers after they were either robbed or legitimately visited were compared, and three levels of nectar robbing were created to detect the effects of nectar robbing on pollinator behaviour and plant reproduction. Nectar replenishment did not differ between flowers that had been robbed or legitimately visited. Neither fruit set nor seed set was significantly affected by nectar robbing. In addition, nectar robbing did not significantly affect visitation rate, flowers visited within a plant per foraging bout, or flower handling time of the legitimate pollinators. However, a tendency for a decrease in relative abundance of the pollinator B. religiosus with an increase of nectar robbing was found. Nectar robbing did not affect female reproductive success because nectar replenishment ensures that pollinators maintain their visiting activity to nectar-robbed flowers. Nectar replenishment might be a defence mechanism against nectar robbing to enhance reproductive fitness by maintaining attractiveness to pollinators. Further studies are needed to reveal the potential for interference competition among bumble bees foraging as robbers and legitimate visitors, and to investigate variation of nectar robbing in communities with different bumble bee species composition.

Relationships among floral VOC emissions, floral rewards and visits of pollinators in five plant species of a Mediterranean shrubland

Background and aims – In plant-pollinator communities seasonal changes in the abundance of pollinators lead to seasonal changes in competition among flowering plants for their services. Here we address the following question: Do flowers of a given species produce more olfactory signals (emissions of volatile compounds) and rewards (nectar and pollen) during the phase(s) of the flowering period within which they have to maximally compete with the signals and rewards of other co-flowering species in the community, compared to the amount of signals and rewards produced during the period(s) with less floral competition? Methods – We analysed the floral emission rates of biogenic volatile organic compounds by gas chromatography and proton transfer reaction mass spectrometry, the visitation rates of pollinators, and the availability of nectar and pollen during the flowering periods of five species to test whether floral rewards and signals would decrease with an increase in pollinator visitation rates during late spring and early summer, i.e. coinciding with decreasing competitive pressure for the services of pollinators. Key results – The results indicate that phenological patterns in the production of rewards are only present at the species level in those species with long flowering periods or with matching periods of changes in pollinator populations. The capacity of emitting isoprenoids and oxidised volatile organic compounds, however, did not present significant patterns during the flowering period in any of the five species studied. Conclusions – The results support the hypothesis of a decreasing competitive pressure for the attraction of pollinators that may drive a decrease in floral investment in rewards but not an accompanying decrease of the capacity of emitting volatile olfactory signals in a species with long flowering period. However, the negative correlation between nectar production and visitation rates may be reinforced by the opposite responses of these variables to climatic conditions. This fact makes difficult to discern possible evolutionary forces tending to decrease rewards from plastic responses to changing environmental conditions in that part of the flowering period in which pollinator visitation rates are higher .

Nectaries and male-biased nectar production in protandrous flowers of a perennial umbellifer Angelica sylvestris L. (Apiaceae)

Nectar is the most common floral pollinator reward. In dichogamous species, floral nectar production rates can differ between sexual phases. We studied the structure of nectaries located on the stylopodium and nectar production in protandrous umbellifer Angelica sylvestris. Our study species produced nectar in both floral sexual phases. Nectar sugar concentration was low (on average 22 ± 11 %, mean ± SD) and the nectar hexose rich and composed of sucrose, glucose, fructose and a small amount of amino acids, including β-alanine, a non-protein amino acid. Although nectar composition and sugar concentration varied little between floral sexual phases, nectar production showed a threefold reduction during the stigma receptive period. This is in contrast to other studies of Apiaceae that have reported female-biased nectar production, but in the direction predicted by plant sexual selection theory, suggesting that in pollen-unlimited species, floral rewards mainly enhance male reproductive success. The structure of the nectary was similar at the two sexual stages investigated, and composed of a secretory epidermis and several layers of nectariferous and subsecretory parenchyma. The nectary cells were small, had large nuclei, numerous small vacuoles and dense, intensely staining cytoplasm with abundant endoplasmic reticulum, mitochondria and secretory vesicles. They contained abundant resin-like material that may potentially act as defence against microbes. Starch was rarely observed in the nectary cells, occurring predominantly at the female stage and mainly in guard and parenchyma cells in close proximity to stomata, and in subsecretory parenchyma. The main route of nectar release in A. sylvestris seems to be via modified stomata.

Effects of nectar robbing on pollinator behavior and plant reproductive success of Pitcairnia angustifolia (Bromeliaceae)

AbstractNectar robbers may have direct and indirect effects on plant reproductive success but the presence of nectar robbing is not proof of negative fitness effects. We combined census data and field experiments to disentangle the complex effects of nectar robbing on nectar production rates, pollinator behavior, pollen export, and female reproductive success of Pitcairnia angustifolia. Under natural conditions flowers were visited by four different animal species including a robber‐like pollinator and a secondary robber. Natural levels of nectar robbing ranged from 40 to 100%. Natural variation in nectar robbing was not associated with fruit set in any year whereas seed set was weakly positively associated for 1 year only. Artificial nectar robbing did not increase nectar production or concentration, did not affect the behavior of long‐billed hummingbirds, and when faced with artificially robbed flowers, these visitors behaved as secondary nectar robbers. The number of stigmas within a patch that received pollen dye analogs and the average distance traveled by these analogs were not significantly different between robbing treatments (robbed flowers versus unrobbed flowers), but the maximum distance traveled by these pollen analogs was higher when nectar robbing was not prevented. Overall, the proportion of robbed flowers on an inflorescence had a neutral effect to a weak positive effect on the reproduction of individual plants (i.e. positive association between nectar robbing and fruit set in 2002) even when it clearly changed the behavior of its most efficient pollinator potentially increasing the frequency of nectar robbing within a plant.

The biology of flowering of winter aconite (Eranthis hyemalis (L.) Salisb.)

&lt;i&gt;Eranthis hyemalis&lt;/i&gt; belongs to the Ranunculaceae family whose representatives enrich early spring pollen flow and nectar for pollinating insects. Flowering biology and morphological characteristics flowers of winter aconite were studied. The forage value was estimated as the rate of nectar production. Observations were carried out between 2008 and 2011 in the Botanical Garden of the Maria Curie-Skłodowska University located in the Lublin area. In the conditions of Lublin, flowering of winter aconite plants started at the beginning of February and lasted until the end of March. The seasonal bloom dynamics was strongly affected by maximum temperatures, which intensified flower blooming, and snowfalls which hampered this process. During the day, flowers opened between 8.00 am and 3.00 pm, but the highest intensity was between 10.00 am and 12.00 am. The process of pollen release, with the average number of 29 stamens shedding pollen in the flowers, lasted from 2 to 3 days. During the day the largest number of anthers opened at noon hours, between 11.00 am and 1.00 pm, though a certain rise in this number was also observed in the morning hours between 8.00 and 9.00 am. &lt;i&gt;Eranthis hyemalis&lt;/i&gt; flowers develop funnel-shaped nectaries, on average 3-6 per flower. The determined amount of nectar per flower was 1.23 mg, while the concentration of sugars in it averaged 72.11%. The weight of nectar sugar per flower was 0.88 mg.

The structure of some floral elements and the nectar production rate of Polemonium caeruleum L.

The present study, carried out in the period 2008 - 2009, covered some morphological and anatomical features of the flowers of &lt;i&gt;Polemonium caeruleum&lt;/i&gt; L. and their nectar production rate in the climatic conditions of the Lublin region. Observations were made with stereoscopic, light and scanning electron microscopy. Nectar production in the flowers was determined using the pipette method. The flowers of &lt;i&gt;Polemonium caeruleum&lt;/i&gt; develop a calyx covered by an epidermis with numerous non-glandular and glandular trichomes. The secretory trichomes are composed of a several-celled stalk and a four-celled head. At the boundary of the corolla tube and the lobes, there is white colouration with violet nectar guides. The epidermis in this region produces several-celled living trichomes that close the entry into the corolla tube, thereby protecting the nectar accumulated in it. These hairs are at the same time glistening colour attractants for insects. The tripartite stigma of the pistil is covered, from the adaxial side, by unicellular papillae with striated cuticular ornamentation, growing at high density. Around the ovary there is located a nectariferous disc, in the form of a free projection, which secrets nectar with sugar concentration of 29 - 52% and sugar weight ranging 1.1 - 1.8 mg/flower.

The structure of secretory tissue of the stigma and septal nectaries as well as nectar secretion of flowers of Hosta fortunei Baker L. H. Bailey (Funkiaceae)

A study of &lt;i&gt;Hosta fortunei&lt;/i&gt; Baker L. H. Bailey (Funkiaceae) flowers was conducted in the years 2007 - 2008. The flower life span and flowering duration as well as the nectar production rate were determined. The structure of the tissues of the stigma and nectary was investigated using stereoscopic, light and scanning electron microscopy (SEM). The plants flowered over a period of five weeks. Flowers of &lt;i&gt;H. fortunei&lt;/i&gt; lived two days, on the average. Developed a pistil with an elongated ovary terminating in a discal stigma. On the surface of the stigma, unicellular glandular trichomes grew densely, composed of a stalk with a length of 113 - 213 µm and a head which was characterised by a large diameter range of 54 - 96 µm. The cuticle on the apical surface of a part of the trichomes was smooth, whereas it was striated on the stalk. Their protoplast was characterised by dense cytoplasm and weak vacuolisation. In the head of the trichomes fatty substances were accumulated. Septal nectaries occurred in the ovary of the superior pistil. Nectar was exuded onto the surface through three openings, situated in the upper part of the ovary of the pistil. At these places, epidermal cells formed a smooth or slightly wrinkled cuticle. The outer walls of the cells of the epidermis covering the duct accumulating nectar were thick. The glandular tissue of the nectary was made up of 2 layers of different-shaped, thin-walled cells and a deeply stained protoplast. They contained dense cytoplasm and a large, frequently lobate nucleus. At the final stage of secretion, fine vacuoles were observed in the cytoplasm of the glandular cells. Nectar secretion was abundant. In its initial stage, secretion droplets, increasing during the activity of the glandular tissue, were observed on the epidermis surface around the nectar openings. The weight of nectar from 10 flowers was 92.41 mg. The sugar concentration in the nectar was within a range of 23% - 30%, with an average value of 26%. Sugar yield was 23.83 mg/from 10 flowers.

Nectary structure and nectar secretion of Echium russicum J. F. Gmel. flowers

In this study, the micromorphology of nectaries in &lt;i&gt;Echium russicum&lt;/i&gt; J. F. Gmel. flowers was determined by using scanning electron microscopy (SEM) and their anatomy by using light microscopy (LM). The rate of nectar production of flowers and sugar concentration in nectar were investigated. The nectary gland is located below the ovary of the pistil. It is composed of 4 parts corresponding to the parts of the ovary. The widest regions of the nectar-producing tissue are situated by the furrows separating the adjacent parts of the ovary. Nectar is secreted through anomocytic stomata, located only in the lower part of the nectary. The stomata were distributed evenly or they formed clusters of 2-3. The average number of stomata on the surface of the whole nectary was 184. At the nectar secretion stage, open and closed, as well as not fully mature stomata were observed. The orientation of most of the stomata was parallel to the nectary base. The cuticle surface of the cells of the upper and lateral part of the nectary was smooth, whereas in the region producing stomata it showed various folds facilitating the retention of nectar. The flowers produced nectar throughout the flowering period. The weight of nectar secreted throughout the lifetime of ten flowers was, on the average, 20 mg, with the concentration of sugars of 58% and their weight reaching 17 mg.

Effect of boreal forest logging on nectar production of four understory herbs

The rate of floral nectar production, an important trait for supporting populations of pollinators, is known to be affected by local environment. This study examines the effect, 9 years after an anthropogenic disturbance—variable retention logging,—on the rate of daily nectar production of four common herbs ( Chamerion angustifolium, Delphinium glaucum, Mertensia paniculata and Vicia americana) in the boreal forest of Alberta, Canada. We measured daily nectar production rates 9 years after experimental logging in three treatments: clear cuts (all merchantable trees removed), 50% of trees retained, and unlogged controls. Per-flower nectar production rate was unaffected by logging for C. angusifolium, D. glaucum, and M. paniculata, and lower in unlogged controls than in the 50% logging treatment for V. americana. Overall, we found a surprising robustness of nectar production of these herbaceous plants to the physical and environmental changes following logging. While other research has shown boreal forest logging to affect the densities of understory herbs, the per-flower nectar production in boreal forest understory herbs appears to be relatively insensitive to this disturbance.

Female-biased nectar production in the protandrous, hermaphroditic shrub Salvia hierosolymitana (Lamiaceae)

Flowering progresses upward along vertical inflorescences in the protandrous dichogamous shrub Salvia hierosolymitana (Boiss.). Flowers’ gender nectar production rates and their vertical distribution were recorded in two populations (northern and central Israel) over 3 years. Female-phase flowers produced significantly more nectar than male-phase flowers and were more abundant at the inflorescences’ base. Thus, nectar availability gradually decreases along inflorescences. Female-biased nectar production can benefit plants by increasing pollinator visits to female-phase flowers, enhancing pollination success when pollen is scarce. In congruence with this hypothesis, the following observations suggest that pollen in S. hierosolymitana may be in short supply: (1) freshly dehisced anthers contained 40% of sterile pollen; (2) pollen counts on female-phase stigmas were low (mean ± s.e. 11.6 ± 1.56); and (3) counts of germinated pollen tubes at the pistils’ base were even lower (5.02 ± 0.54). The nectar gradient along the inflorescence may also be adaptively beneficial in other aspects. Foraging insects that follow this gradient are expected to move from female-phase flowers near the inflorescences’ base, to male-phase flowers closer to the top. Thus, reducing the risk of geitonogamy and promoting outcrossing while moving from male-phase flowers of one individual to female-phase flowers of another.

Pollination and nectar production of Psittacanthus schiedeanus (Loranthaceae) in central Veracruz, Mexico

We assessed nectar production patterns, the breeding system, and overall pollinator dependence of Psittacanthus schiedeanus (Schlecht. &amp; Cham.) G.Don (Loranthaceae), a mistletoe species that blooms in the late summer of the eastern cloud forests of Mexico and whose flowers are mainly visited by hummingbirds. Despite differences in nectar production rates over the lifespan of a flower, the daily nectar secretion of 3.6-7.2 mg sugar/flower/day was high compared to other hummingbird-adapted plant species. Hand-pollination experiments showed that this plant is self-compatible, with only a slight advantage of cross- (xenogamous) and geitonogamous hand-pollinated flowers over autonomous hand-pollinated flowers. Hence, the high production of nectar by P. schiedeanus flowers represents an important ecosystem resource that may mediate interactions with a wide variety of floral visitors. Although P. schiedeanus set selfed fruits autonomously, this plant requires hummingbirds to achieve its full reproductive potential.